Página 1 dos resultados de 335 itens digitais encontrados em 0.002 segundos

Contribuições ao estudo das cúpulas metálicas ; Contributions to the study of the metallic domes

Santos, Luciano Barbosa dos
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 07/07/2005 PT
Relevância na Pesquisa
37.44%
Este trabalho aborda, de uma forma geral, os sistemas estruturais normalmente adotados no projeto de cúpulas metálicas. Foi dado ênfase a um arranjo derivado do sistema Schwedler, recentemente utilizado em projetos desenvolvidos no interior do estado de São Paulo. O trabalho pode ser divido em duas partes, a primeira delas versando sobre as ligações que compunham o sistema estrutural estudado, e a segunda versando sobre a influência dessas ligações no comportamento da estrutura e sobre a influência da forma de contraventamento. As ligações foram estudadas sob dois aspectos diferentes, que foram: a) revisão e aperfeiçoamento dos critérios de dimensionamento adotados em algumas ligações, e b) proposição de modelos para descrição do comportamento momento-rotação de ligações com dupla tala de alma parafusada e de aparelhos de apoio. A influência do tipo de contraventamento e da rigidez das ligações foi investigada por meio do efeito exercido nos deslocamentos verticais e na distribuição de esforços internos da estrutura. Para tanto, foram utilizados programas computacionais de uso já consagrado, cujos resultados foram comparados entre si.; In a general way, this work deals with structural systems usually adopted in the project of metallic domes. Emphasis was given to a derived arrangement derived of the Schwedler system...

Preparação e caracterização de nanoestruturas de carbono contendo nitrogênio; Synthesis and characterization of carbon nanostructires containing nitrogen

Pablo Jenner Paredez Angeles
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 10/07/2007 PT
Relevância na Pesquisa
27.44%
Nesta tese são apresentados os efeitos nas propriedades estruturais, eletrônicas e de emissão eletrônica por efeito de campo elétrico induzidos pela incorporação de nitrogênio em nanoestruturas de carbono. As nanoestruturas de carbono contendo nitrogênio foram preparadas por pulverização catódica (sputtering) de um alvo de grafite assistido, ou não, por um feixe iônico. A técnica permite atuar sobre os parâmetros de deposição induzindo mudanças nas propriedades estruturais, eletrônicas e de emissão eletrônica por efeito de campo elétrico. O papel do hélio na formação de nanoes-truturas de carbono contendo nitrogênio foi também explorado, mostrando que o gás nobre promove maior incorporação de nitrogênio. Isto é provavelmente devido à relativa alta condutividade térmica que apresenta o hélio, propriedade que modifica a cinética do crescimento das nanoestruturas. O estudo realizado permitiu entender o mecanismo de formação das nanoestruturas, mostrando que primeiramente o carbono alcança as partículas de Ni por difusão até a saturação do metal, iniciando a formação das camadas grafíticas sobre a partícula de Ni, camadas que foram observadas por microscopia eletrônica de transmissão de alta resolução. O estudo mostra...

Modelagem matemática da evolução de domos salinos sua influência na perfuração de poços de petróleo; Mathematical modeling of the evolution of salt domes and its influence in drilling oil wells

Eduardo Salmazo
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 26/02/2013 PT
Relevância na Pesquisa
26.98%
Neste trabalho discute-se os desafios associados à atividade de perfuração de poços de petróleo através de formações afetadas pela presença de domos salinos. Domos salinos podem induzir grandes tensões nas formações subjacentes e adjacentes, impondo a necessidade de um planejamento específico para a perfuração e manutenção de poços de petróleo. Durante a perfuração, em frente à zonda de sal, há relatos de problemas de aprisionamento de coluna, dissolução de sal no fluido de perfuração, ocasionando a formação de batentes mecânicos e cavernas. Há ainda, nas formações que rodeiam um domo salino, devido à alterações no campo de tensões, problemas de instabilidade nas paredes do poço aberto e formação de zonas anormalmente prossurizadas. Após o revestimento do poço, há casos de colapso do revestimento. Para prever e mitigar os riscos associados à essa atividade é de fundamental importância o entendimento dos fenômenos físicos que o ocasionam. Com essa finalidade, foi feito um estudo à respeito de tais mecanismo físicos como fluência e instabilidade hidrodinâmica, mais especificamente a instabilidade de Rayleigh-Taylor. Desenvolveu-se, a partir de tal estudo, um modelo analítico para prever o desenvolvimento de um domo salino e discutiu-se a forma como este pode interferir em parâmetros importantes para a atividade de perfuração como...

Vibrotactile sensitivity of slowly adapting type I sensory fibres associated with touch domes in cat hairy skin.

Vickery, R M; Gynther, B D; Rowe, M J
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //1992 EN
Relevância na Pesquisa
27.26%
1. Recordings were made from single slowly adapting type I (SAI) afferent fibres associated with touch domes in the cat hairy skin. Controlled vibratory stimuli were used first, to characterize the precision with which these SAI afferents reflect the temporal aspects of vibrotactile stimuli, and second, to determine whether earlier disparate reports of SAI responsiveness to vibration may be attributable to highly specific stimulus requirements. 2. Eighteen SAI fibres from femoral cutaneous nerve branches were examined; each was associated with one to three touch domes. SAI responses to both steps and sinusoidal vibration (1-1.5 s in duration) were affected profoundly by both probe size and position. Punctate stimulus probes (250 microns) produced much higher response levels and steeper stimulus-response relations than those elicited with large (2 mm) probes, probably on account of focal distortion created within the dome by the smaller probes. SAI sensitivity to vibration was also affected markedly by the amplitude of any pre-indentation on which the vibration was superimposed; sensitivity was much lower when the pre-indentation exceeded 100 microns, in particular with larger stimulus probes. 3. Measures of both vibration sensitivity and the precision of impulse patterning demonstrated that...

Transepithelial transport in cell culture. A theoretical and experimental analysis of the biophysical properties of domes.

Tanner, C; Frambach, D A; Misfeldt, D S
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1983 EN
Relevância na Pesquisa
27.64%
Dissociated cells of transporting epithelia, when cultured on an impermeant substratum, form polarized monolayers frequently characterized by the presence of domes. If the assumption is made that the monolayer exhibits a uniform stretch modulus of elasticity and tension of cell-dish adhesion, Ta, then biophysical properties of the epithelium can be predicted. We have shown that for such epithelia, domes should (a) have circular bases, (b) be sections of spheres with a constant height to radius, h/r, ratio, (c) have a dome-wall tension, Tw, that is constant, and (d) have a dome volume that is a function of radius alone. Additionally, a Laplace equation derived for this geometry predicted the hydrostatic pressure from within to outside domes as a decreasing function of radius alone. By microscopy, domes had predominantly circular bases and were found to be sections of spheres with a constant height, h, to radius, r, ratio of 0.684. Using the Laplace equation derived for this geometry and measurements of delta P and r, the tension of cell-dish adhesion, Ta, and dome-wall tension, Tw, were found to be constants of 6.60 and 7.08 torr, respectively. Combining the constants for Ta and h/r ratio, and the fact that domes are sections of spheres...

Electrical currents flow out of domes formed by cultured epithelial cells

Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 01/10/1984 EN
Relevância na Pesquisa
27.86%
Domes are localized areas of fluid accumulation between a cultured epithelial cell monolayer and the impermeable substratum on which the cells are cultured in vitro. Dome formation has been documented in a variety of epithelial cell lines that retain their transepithelial transport properties in vitro. However, it is not known whether domes are predominantly areas of specific active transport, or, alternatively, are predominantly areas of relative weak attachment to the culture surface. In the present study we adapted a vibrating microelectrode, which can detect small currents flowing in extracellular fluid, to determine if current was flowing into or out of domes and thereby to determine if domes were specialized areas of active transport. We used alveolar type II cells as the main epithelial cell type because they readily form domes in vitro and because they transport sodium from the apical to the basal surface. We found that electrical current flowed out of domes. The direction of the current was independent of the size of a dome, of the age of an individual dome, and of the number of days in primary culture for alveolar epithelial cells. This current was inhibited by amiloride and ouabain and was dependent on sodium in the medium. We made similar observations (outward current from domes which is blocked by amiloride and by sodium substitution) with domes formed by the Madin-Darby canine kidney cell line. The data support the hypothesis that sodium is transported across the entire monolayer and leaks back mainly through the domes. We conclude that domes in epithelial monolayers are not predominantly special sites of active transport but are more likely simply areas of weak attachment to the substratum.

Endothelial Domes Encapsulate Adherent Neutrophils and Minimize Increases in Vascular Permeability in Paracellular and Transcellular Emigration

Phillipson, Mia; Kaur, Jaswinder; Colarusso, Pina; Ballantyne, Christie M.; Kubes, Paul
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 20/02/2008 EN
Relevância na Pesquisa
26.98%
Local edema, a cardinal sign of inflammation associates closely with neutrophil emigration. Neutrophil emigration has been described to occur primarily through endothelial junctions (paracellular) and more rarely directly through endothelial cells (transcellular). Recently, we reported that unlike in wild-type (wt) mice, Mac-1-/- (CD11b) neutrophils predominantly emigrated transcellularly and was significantly delayed taking 20–30 min longer than the paracellular emigration (wt). In the present study we noted significant anatomical disruption of the endothelium and hypothesized that transcellular emigration would greatly increase vascular permeability. Surprisingly, despite profound disruption of the endothelial barrier as the neutrophils moved through the cells, the changes in vascular permeability during transcellular emigration (Mac-1-/-) were not increased more than in wt mice. Instead increased vascular permeability completely tracked the number of emigrated cells and as such, permeability changes were delayed in Mac-1-/- mice. However, by 60 min neutrophils from both sets of mice were emigrating in large numbers. Electron-microscopy and spinning disk multichannel fluorescence confocal microscopy revealed endothelial docking structures that progressed to dome-like structures completely covering wt and Mac-1-/- neutrophils. These domes completely enveloped the emigrating neutrophils in both wt and Mac-1-/- mice making the mode of emigration underneath these structures extraneous to barrier function. In conclusion...

Dual Innervation of Neonatal Merkel Cells in Mouse Touch Domes

Niu, Jingwen; Vysochan, Anna; Luo, Wenqin
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 17/03/2014 EN
Relevância na Pesquisa
27.26%
Merkel cell-neurite complexes are specialized mechanosensory end organs that mediate discriminative touch sensation. It is well established that type I slowly adapting (SAI) mechanoreceptors, which express neural filament heavy chain (NFH), innervate Merkel cells. It was previously shown that neurotrophic factor NT3 and its receptor TrkC play crucial roles in controlling touch dome Merkel cell innervation of NFH+ fibers. In addition, nerve fibers expressing another neurotrophic tyrosine receptor kinase (NTRK), Ret, innervate touch dome Merkel cells as well. However, the relationship between afferents responsive to NT3/TrkC signaling and those expressing Ret is unclear. It is also controversial if these Ret+ fibers belong to the early or late Ret+ DRG neurons, which are defined based on the co-expression and developmental dependence of TrkA. To address these questions, we genetically traced Ret+ and TrkC+ fibers and analyzed their developmental dependence on TrkA. We found that Merkel cells in neonatal mouse touch domes receive innervation of two types of fibers: one group is Ret+, while the other subset expresses TrkC and NFH. In addition, Ret+ fibers depend on TrkA for their survival and normal innervation whereas NFH+ Merkel cell innervating fibers are almost unaltered in TrkA mutant mice...

Equilibrium analysis of masonry domes

Lau, Wanda W
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 172 p.; 8115849 bytes; 8120079 bytes; application/pdf; application/pdf
ENG
Relevância na Pesquisa
27.88%
This thesis developed a new method to analyze the structural behavior of masonry domes: the modified thrust line analysis. This graphical-based method offers several advantages to existing methods. It is the first to account for the ability of domes to achieve a range of internal forces, gaining potentially an infinite number of equilibrium solutions that could not be derived otherwise. This method can also analyze non-conventional axisymmetrical dome geometries that are difficult or impossible to analyze with existing methods. Abiding by limit state conditions and the principles of the lower bound theorem, the modified thrust line method was used to ascertain the theoretical minimum thrust of spherical and pointed domes, a parameter that was previously unsolved. Several methods to estimate minimum thrust to-weight ratio were provided. For spherical domes, this ratio may be estimated as -0.583[alpha] + 1.123; for pointed domes, the estimated ratio is 0.551[delta] -1.061[delta]/[alpha] -0.615[alpha] + 1.164, where [alpha] and [delta] are the embrace and truncating angles, respectively.; (cont.) From the results, salient relationships between minimum thrust and dome geometry were derived, including an inverse relationship between the minimum thrust and the thickness-to-radius ratio...

Geografía de la vegetación de las coladas domáticas del atrio de las Cañadas del Teide (Tenerife. I. Canarias)

Arozena Concepción, Mª Eugenia; Beltrán Yanes, Esther
Fonte: Universidad de Alcalá. Servicio de Publicaciones Publicador: Universidad de Alcalá. Servicio de Publicaciones
Tipo: Artigo de Revista Científica Formato: 3178553 bytes; application/pdf
SPA
Relevância na Pesquisa
26.98%
El principal condicionante de la geografía del matorral del Parque Nacional del Teide es la geomorfología, y los rasgos de las coladas domáticas del atrio oriental de Las Cañadas constituyen un magnífico ejemplo de esta relación. La estructura morfológica de estas corrientes lávicas es variable y determina diferentes tipos de microtopografías y distintas granulometrías superficiales que dificultan o favorecen, según los casos, la colonización vegetal y siempre condicionan las características del matorral. El resultado es un complejo mosaico de tipos de vegetación diferenciados por su nivel de continuidad, su grado de recubrimiento, su composición florística y la importancia relativa de los taxones mejor representados.; The main factor of the geography of the Teide National Park scrub is the geomorphology and the features of the oriental atrium domes lava flows of Las Cañadas constitute a magnificent example of this relationship. The morphologic structure of these lava flows is variable and it determines different microtopography and different superficial grains that hinder or they favours, according to the cases, the plant colonization and always condition the characteristics of the scrub. The result is a complex mosaic of vegetation types differed by its level of continuity...

The Domes Which Are Characeristic of All Coptic Churches.

Leeder, S.H.
Fonte: Electronic version published by Rice University, Houston, Tx Publicador: Electronic version published by Rice University, Houston, Tx
Tipo: illustrations; StillImage
ENG
Relevância na Pesquisa
26.98%
Caption: "The Domes Which Are Characteristic of All Coptic Churches. At the Desert Monastery of Anba Bishai"; Domed structure with a man in a pith helmet standing in front. Black- and- white photograph.

Domes of Damascus.

Tyrwhitt, Walter S.S.
Fonte: Electronic version published by Rice University, Houston, Tx Publicador: Electronic version published by Rice University, Houston, Tx
Tipo: illustrations; StillImage
ENG
Relevância na Pesquisa
27.26%
Caption: "Domes of Damascus."; A street lined with domes and minarets. Painting.

Development of construction techniques in the Mamluk domes of Cairo

Cipriani, Barbara
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 117 leaves; 13487870 bytes; 13492807 bytes; application/pdf; application/pdf
ENG
Relevância na Pesquisa
26.98%
This dissertation reconstructs the building features, the construction methods and the esthetic and structural changes of the Mamluk Mausolea in Cairo (1250-1517 A.D.); a special attention is dedicated to the domes that cover all the Mausolea and that represent an example of high expertise in Mediaeval architecture. This works document several stages of their construction from the Mausoleum of As- Sawabi, 1285 A.D. to the Funerary Complex of Amir Qurqumas, 1506 A.D. through bibliographic sources, photographic material and restoration reports collected in several libraries and archives where information on the topic is stored. Moreover, three Mausolea belonging to the period of construction in stone: Umm Sultan Sha'ban (1369 A.D.), Farag Ibn Barquq (1389-1411 A.D.) and Amir Khayer Bek (1502 A.D.) are fully documented with survey on site, technical drawing and structural analysis.; (cont.) Through a detailed analysis of the Mausolea, this work aims to answer to wider questions, such as the role of the patronage in the changes of the architectural features, the differences and the similarities in the construction methods and in the structural behavior between complexes belonging to distinct moment of Mamluk History and the transmission of knowledge in the construction world of Mamluk Cairo.; by Barbara Cipriani.; Thesis (S.M.)--Massachusetts Institute of Technology...

M cells and granular mononuclear cells in Peyer's patch domes of mice depleted of their lymphocytes by total lymphoid irradiation.

Ermak, T. H.; Steger, H. J.; Strober, S.; Owen, R. L.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /03/1989 EN
Relevância na Pesquisa
27.55%
The cytoarchitecture of Peyer's patches that were depleted of their lymphocytes by total lymphoid irradiation (TLI) was examined with particular attention to the effects on M cells in the follicle epithelium and on mononuclear cells in follicle domes underlying the epithelium. Five-month-old, specific pathogen-free Balb/c mice were irradiated with 200-250 rad/day, five times a week to a total dose of 3400-4250, and their Peyer's patches were either fixed for electron microscopy or frozen for immunohistochemistry 1-4 days after completion of irradiation. Control mice were examined at the same time intervals. Follicle domes of TLI mice had approximately one fourth the epithelial surface area of domes of control mice. Within the epithelium, lymphoid cells were virtually depleted after TLI, and yet the epithelium contained M cells. In control mice, most M cells were accompanied by lymphoid cells in invaginations of the apical-lateral cell membrane. In TLI mice, most M cells did not have such apical-lateral invaginations and were columnar shaped. Other than lacking lymphocytes, these cells appeared to be mature M cells. Some M cells did have lymphoid cells or granular mononuclear cells below their basal membranes, adjacent to the basal lamina. Below the epithelium...

Phenotypically distinct subpopulations of T cells in domes and M-cell pockets of rabbit gut-associated lymphoid tissues.

Ermak, T H; Steger, H J; Pappo, J
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/1990 EN
Relevância na Pesquisa
27.55%
Follicle epithelium and domes of gut-associated lymphoid tissue (GALT) contain populations of lymphocytes which first contact antigen taken up from the intestine. In order to study the association of lymphocytes with M cells in follicle epithelium, monoclonal antibodies (mAb) were generated by immunizing BALB/c mice with lymphocytes populating GALT domes from NZW rabbits, and their specificity was assessed by immunohistochemistry and flow cytometry. mAb 3C10 (IgM) and 3B6 (IgG3) recognized subpopulations of intraepithelial lymphocytes associated with M cells. mAb 3C10 also identified macrophage-lymphocyte clusters in domes and tangible body macrophages in germinal centres of GALT but did not react with cells in T-dependent areas (TDA) or B cells in follicles. mAb 3B6 recognized lymphocytes in domes and B cells in follicles but not T cells in TDA of GALT. The distribution of 3B6+ cells overlapped with, but was more restricted than, that of Ia+ cells. Analysis of lymphocytes in follicle epithelium showed that greater than 95% of lymphocytes associated with M cells were Ia+. T cells represented approximately 95% of intraepithelial lymphocytes in the appendix and approximately 65% in Peyer's patches. A majority of intraepithelial lymphocytes was recognized by mAb 3B6...

Flux domes in superconducting films without edges

Clem, John R.; Mawatari, Yasunori
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 03/07/2006
Relevância na Pesquisa
27.44%
Domelike magnetic-flux-density distributions previously have been observed experimentally and analyzed theoretically in superconducting films with edges, such as in strips and thin plates. Such flux domes have been explained as arising from a combination of strong geometric barriers and weak bulk pinning. In this paper we predict that, even in films with bulk pinning, flux domes also occur when vortices and antivortices are produced far from the film edges underneath current-carrying wires, coils, or permanent magnets placed above the film. Vortex-antivortex pairs penetrating through the film are generated when the magnetic field parallel to the surface exceeds H_{c1}+K_c, where H_{c1} is the lower critical field and K_c = j_c d is the critical sheet-current density (the product of the bulk critical current density j_c and the film thickness d). The vortices and antivortices move in opposite directions to locations where they join others to create separated vortex and antivortex flux domes. We consider a simple arrangement of a pair of current-carrying wires carrying current I_0 in opposite directions and calculate the magnetic-field and current-density distributions as a function of I_0 both in the bulk-pinning-free case (K_c = 0) and in the presence of bulk pinning...

Attenuation of acoustic waves in glacial ice and salt domes

Price, P. B.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 27/06/2005
Relevância na Pesquisa
27.44%
Two classes of natural solid media (glacial ice and salt domes) are under consideration as media in which to deploy instruments for detection of neutrinos with energy >1e18 eV. Though insensitive to 1e11 to 1e16 eV neutrinos for which observatories (e.g., AMANDA and IceCube) that utilize optical Cherenkov radiation detectors are designed, radio and acoustic methods are suited for searches for the very low fluxes of neutrinos with energies >1017 eV. This is because, due to the very long attenuation lengths of radio and acoustic waves in ice and salt, detection modules can be spaced very far apart. In this paper, I calculate the absorption and scattering coefficients as a function of frequency and grain size for acoustic waves in glacial ice and salt domes and show that experimental measurements on laboratory samples and in glacial ice and salt domes are consistent with theory. For South Pole ice with grain size 0.2 cm at -51 degrees C, scattering lengths are calculated to be 2000 km and 25 km at 10 kHz and 30 kHz, respectively, and the absorption length is calculated to be 9 km at frequencies above 100 Hz. For NaCl (rock salt) with grain size 0.75 cm, scattering lengths are calculated to be 120 km and 1.4 km at 10 kHz and 30 kHz, and absorption lengths are calculated to be 30...

Icosadeltahedral geometry of fullerenes, viruses and geodesic domes

Siber, Antonio
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 22/11/2007
Relevância na Pesquisa
27.26%
I discuss the symmetry of fullerenes, viruses and geodesic domes within a unified framework of icosadeltahedral representation of these objects. The icosadeltahedral symmetry is explained in details by examination of all of these structures. Using Euler's theorem on polyhedra, it is shown how to calculate the number of vertices, edges, and faces in domes, and number of atoms, bonds and pentagonal and hexagonal rings in fullerenes. Caspar-Klug classification of viruses is elaborated as a specific case of icosadeltahedral geometry.

Sucessões vulcânicas, modelo de alimentação e geração de domos de lava ácidos da Formação Serra Geral na região de São Marcos-Antônio Prado (RS); Volcanic succession and feeder systems of acidic lava-domes of Serra Geral Formation in São Marcos-Antônio Prado region, South Brazil

Lima, Evandro Fernandes de; Philipp, Ruy Paulo; Rizzon, Gabriela Cioato; Waichel, Breno Leitão; Rossetti, Lucas de Magalhães May
Fonte: Universidade de São Paulo. Instituto de Geociências Publicador: Universidade de São Paulo. Instituto de Geociências
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; ; Formato: application/pdf
Publicado em 01/08/2012 POR
Relevância na Pesquisa
37.64%
Na região entre São Marcos (RS) e Antônio Prado (RS), a Formação Serra Geral expõe na base uma sucessão de basaltos do tipo pahoehoe sotopostos a derrames ´a´ā. Os primeiros foram gerados por um volume de erupção baixo em um regime de fluxo fechado e colocado em uma paleotopografia plana (< 5° de declividade). A lenta perda de calor deste sistema permite que os fluxos atinjam distâncias da fonte > 100 km. Os tipos ´a´ā foram gerados por descargas dos fluxos superiores às das pahoehoe e transportados em canais abertos, em que o rápido resfriamento limita o deslocamento dos fluxos por longas distâncias da fonte. Ambos são toleíticos de baixo TiO2 e a morfologia dos derrames não pode ser explicada por variações geoquímicas. Acima destes afloram vulcanitos ácidos quimicamente compatíveis com o Grupo Palmas e Subgrupo Caxias. Recentemente, a extração de rochas ornamentais na região expôs as porções internas dos diques de alimentação deste vulcanismo. Observam-se estruturas magmáticas subverticais e verticais que em superfície abasteceram domos de lavas com características exógenas. Propõe-se um modelo para a geração destes envolvendo a ascensão diapírica de magmas ácidos que se tornam vesiculados...

New 40Ar/39Ar ages from the Central Part of the Chiapanecan Volcanic Arc, Chiapas, Mexico

Mora,Juan Carlos; Layer,Paul W.; Jaimes-Viera,María del Carmen
Fonte: Instituto de Geofísica, UNAM Publicador: Instituto de Geofísica, UNAM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2012 EN
Relevância na Pesquisa
27.26%
The Chiapanecan Volcanic Arc (CVA), located in the central portion of the State of Chiapas, is a 150 km long chain of volcanic structures aligned in a NW-SE direction. The central part of the CVA is composed of an irregular northeast-trending alignment of more than 10 volcanic structures, generally centered along NNW-SSE trending faults splayed from the Motagua-Polochic Fault System. Among these structures are seven volcanic domes (Huitepec, Amahuitz, La Iglesia, Mispía, La Lanza, Venustiano Carranza, and Santotón), one explosion crater (Navenchauc), one collapse structure (Apas), and one dome complex (Tzontehuitz). In this work, we report thirteen new 40Ar/39Ar ages of rocks from seven domes that increase the available geochronometric data on Quaternary volcanic activity in the central part of Chiapanecan Volcanic Arc. From the new and previous data, we identified the Tzontehuitz Dome Complex as the oldest volcanic center in the CVA, yielding an age of 2.1 Ma, and the Venustiano Carranza Volcanic Dome as exhibiting the most recent activity in the zone, with an age of 0.225 Ma.